The present invention relates to a stereoscopic instrument and, in particular, but not exclusively, a stereoscopic microscope for providing three-dimensional perception of objects at high magnification powers.
Binocular microscopes are commonly used in a wide range of scientific and industrial fields for inspecting samples with microscopic features. Typically, the principle of operation of the most widely used microscopes is to split a single beam, formed by an objective lens, into two beams, and to form each of the two beams into two images that are presented to the respective left and right eyes of a user. The main benefit of this architecture of microscope is ergonomic; it is more comfortable for a user of such a microscope to have both eyes open and focused to the same distance. However, this type of microscope cannot be called ‘stereoscopic’ since the images presented to each of the eyes of the user are identical.
For stereopsis (the perception of depth) to occur, the human brain relies on various cues contained within the images we see. Some of these cues do not rely on binocular vision; for example, the brain can determine that one object is behind another, even if only one eye is used, when the view of part of the one object is partially obstructed by the other. However, true depth perception, the sense of how far away one point in three-dimensional space is relative to all others, can only be achieved by the brain by utilizing cues that are only available if both eyes are used. The principal such cue is binocular disparity. Binocular disparities are those differences between the left and right retinal images due to the difference in aspect that one eye has with respect to the other, caused by the spatial separation of the eyes. The images formed in each of the eyes are slightly different because the effect of parallax on the image in one eye is different to the effect on the image in the other eye. This difference essentially contains information that the brain can use to perceive relative depth.
GB2379280 describes a method of modifying the microscope architecture described above to provide different images to each of the left and right eyes, the images corresponding to left and right perspective views of objects in the field of view of the objective. Essentially, GB2379280 describes reimaging optics, in each of the left and right optical paths, which form conjugates of the aperture plane of the objective. In these conjugate planes, opaque masks occlude part of the optical beam such that the left optical path transmits a perspective image of the field of view as seen from the left side of the objective aperture, and the right optical path transmits a perspective image of the field of view as seen from the right side of the objective aperture.
While the arrangement described in GB2379280 goes some way to improving the ease with which depth may be perceived, it does not permit accurate perception of depth.
It is an object of the present invention to provide an improved stereoscopic microscope.